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Scientists have cataloged and mapped 6,194 early star-forming clouds in the biggest-ever survey of dense clumps in our Milky Way Galaxy

The survey by University of Arizona's Steward Observatory allows astronomers to better understand the earliest phases of star formation.

The finding is a major step forward in astronomy because it allows astronomers to study the earliest phases of star formation when the gas and dust in the star-forming clouds are just beginning to coalesce, before giving rise to clusters of stars, researchers said.

"All the famous, major regions of star formation in our galaxy have been studied in great detail. But we know very little about what happens in those star-less clumps before proto-stars form, and where," said Yancy Shirley, who led the survey.

The survey provides the first unbiased map of the galaxy that shows where all those regions are throughout the galaxy, in different galactic environments and at different evolutionary stages.

This helps astronomers better understand how the properties of these regions change as star formation progresses.

"For the first time, we have seen this earliest phase of star formation, before a cluster actually forms, in large numbers in an unbiased way," said Shirley.

The star formation rate in the Milky Way was higher in the past, and currently stars form on the order of about one solar mass per year.

"In our survey there seem to be fewer regions that have not yet begun forming stars than those that have, which tells us the earlier phase must be shorter. If that phase lasted much longer, there should be many more of those," Shirley said.

Because the dense accumulations of dust are impervious to light in the visible spectrum, astronomers can't observe them with telescopes detecting light in the visible spectrum such as the Hubble Space Telescope.